Joshua Schrier Helps Discover New Organic Semiconductor

Published on: 08/31/11

If, one day, your iPad rolls up like a newspaper or solar panels are painted on your house, you will have Assistant Professor of Chemistry Joshua Schrier, in part, to thank. The theoretical chemist was part of a group of scientists who recently reported a new organic semiconductor in the August 16 issue of the journal Nature Communications.

Organic semiconductors—carbon-based materials that move electrical charges from one place to another—are the great hope of the future of modern electronics and widespread solar power. Inorganic semiconductors, such as silicon, allow electrons to move quickly (a property known as electron mobility), but are rigid and expensive to grow in high purity. In contrast, organic semiconductors tend to have low mobilities, but can potentially be used on flexible substrates and processed cheaply. Organic semiconductors have been studied since the 1970s, and new material discovered by Schrier and his co-authors at Harvard and Stanford universities is one of the fastest discovered so far.

Schrier initiated the theoretical side of this project back in 2007. He began by working from a model of an organic semiconductor molecule called DNTT, and then considered various compounds possessing chemical and electrical properties that seemed likely to enhance the parent material's performance if they were attached. This led to a collaboration with Harvard Associate Professor of Chemistry Alan Aspuru-Guzik to theoretically compute the molecules.

“Together we were able to make the predictions listed in the paper,” says Schrier. “We had initially tried to publish the theoretical work on its own, but nobody believed us! So we turned to [Stanford] Professor Zhenan Bao's group to synthesize the molecules with high purity and produce the working devices, which turned out even better than we predicted, but it took a few years.”

Their molecule was twice as fast as the original DNTT in conducting electrical current, and according to Science Daily, this new material is more than 30 times faster than the amorphous silicon that is being used in LCD screens now.

It took much less time than expected for the researchers to discover this new material because of Schrier’s predictive approach.

"It would have taken several years to both synthesize and characterize all the seven candidate compounds,” Bao told Science Daily. “With this approach, we were able to focus on the most promising candidate with the best performance, as predicted by theory. This is a rare example of truly 'rational' design of new high performance materials."

Schrier, who is on sabbatical leave this academic year, is continuing the work he started with this project. Two of his students, Malenca Logan '14 and Arman Terzian '14, spent this past summer applying the same computational strategy to two new classes of organic semiconductor molecules. And another one of Schrier's students, Anna Brockway '12, recently published with his Harvard collaborators in The Journal of Physical Chemistry Letters, detailing the theory-driven search for organic solar cell material.

“We are trying to understand how molecular structure influences various properties relevant to charge transport in these materials and devise simple ‘rules of thumb’ that will allow us to speed up our search for new molecules,” says Schrier. In the meantime, though, “this work validates our general theoretical approach, so maybe [in the future] people will believe our predictions.”